Background removal

ABSTRACT

A METHOD OF PROVIDING AN IMAGE IN AN ELECTROSTATIC PROCESS WHICH IS SUBSTANTIALLY FREE OF BACKGROUND COMPRISING THE ELIMINATION OF BACKGROUN BY ADHESIVE RETENTION OF BACKGROUND UTILIZING A TACKY OR TACKIFIABLE MEMBER.

United States Patent 3,682,677 BACKGROUND REMOVAL Robert W. Gundlach, Victor, and Warren L. Rhodes, Rochester, N.Y., assignors to Xerox Corporation, Rochester, N.Y. No Drawing. Filed Oct. 1, 1969, Ser. No. 862,971 Int. Cl. 603g 13/00 US. Cl. 117-175 26 Claims ABSTRACT OF THE DISCLOSURE A method of providing an image in an electrostatic process which is substantially free of background comprising the elimination of background by adhesive retention of background utilizing a tacky or tackifiable member.

BACKGROUND OF THE INVENTION This invention relates to the art of imaging and more specifically to an improved xerographic system.

In the well-known xerographic process described in the US. Pat. 2,297,691, a base plate of relatively low electrical resistance such as metal, paper, etc. having a photoconductive insulating layer thereon is electrostatically chargedd in the dark using conventional methods. The charged coating is then exposed selectively to actinic radiation. Upon exposure the charged plate becomes conductive causing the charges to leak off rapidly to the base plate in proportion to the intensity of the light to which any given area is exposed. After such exposure, the coating is developed by contacting with an electroscopic marking material in the dark. The marking particles attach to the areas where the electrostatic charges remain, forming a powder image corresponding to the electrostatic image. The powder image may then be transferred to a receiver sheet resulting in a positive or negative print, as the case may be, having excellent detail and quality. Alternatively, where the xerographic plate is relatively inexpensive, as is the case with photoconductorbinder coated paper, it may be desirable to fix the powder image directly to the plate itself.

Various methods are employed in the development of exposed xerographic plates such as powder cloud development, touchdown, brush or magnetic brush and cascade with electroscopic marking materials among others. It has been found that whatever the method of development employed undesirable background or imaging noise results. This noise in addition to producing unsatisfactory images in a given situation may eliminate the xerographic process from consideration in applications where such noise, however slight, is unacceptable. Numerous approaches have been taken and attempts made to reduce this noise to acceptable levels and, in some situations, to eventually eliminate the noise completely. The use of especially developed toners or other electrostatic marking materials in connection with electrostatic transfer and careful control of the development process have succeeded in reducing in some instances the levels of noise experienced in the xerographic process, However, though through the employment of any one of a combination of the above methods the levels of noise in a particular application may be significantly reduced, this image noise is not in most instances effectively eliminated.

SUMMARY OF THE INVENTION It is, therefore, an object of this invention to provide a process whereby image noise in an electrostatic process is effectively eliminated.

It is a further object of this invention to provide animproved xerographic imaging system which will overcome the above noted disadvantages.

Still a further object of this invention is to provide a novel xerographic process wherein images free of background may be produced.

The foregoing objects and others are accomplished in accordance with the present invention, generally speaking, by providing a method of transferring a developed electrostatic image from its support for example a photoconductive plate which is precoated prior to imaging and development with a thin tacky layer. Due to the presence of the tacky coating on the surface of the photoconductive layer, the tacky surface is able to hold background or noise and transfer a high contrast image.

The photoconductive surface of a xerographic imaging membed is coated with a tacky or a tackifiable material. The imaging member is then charged, exposed and developed using the well-known techniques of xerography as outlined in US. Pat. 2,297,691. When the image is transferred using a suitable method, for example, electrostatic transfer employing conventional methods, it is found that noise which represents an ordinarily thin layer of electrostatic imaging material is retained by reason of its intimate association with the tacky material or substance and the imaged electrostatic marking material in immediate contact with the adhesive or tacky material is retained while the remainder of the imaged electrostatic marking material not in immediate contact with the tacky substance is transferred, with the final image being free of background. In an alternative embodiment of the process of the present invention, a technique is provided which is compatible with a recyclicable plate or drum comprising the transfer of a powder xerographic image electrostatically to a tacky or tackifiable intermediate substrate. The imaging powder or toner in immediate contact with the tacky surface of the intermediate substrate representing both imaged and non-imaged toner adheres to the surface of the tacky intermediate allowing the remainder of the thicker layered toner in the image areas to separate and transfer a noise free image to a receiving surface. In this embodiment initially both background and image are transferred to the tacky intermediate substrate, the background being retained by the intermediate member, allowing a background free image to transfer to the final receiving member. After use, the intermediate member may be discarded or, instead, renewed by cleaning, using suitable methods and recoating with the tacky or tackifiable material.

When the electrostatic transfer is not desirable or available still another embodiment of the process of the present invention may be employed. After the photoconductive recording member is charged, exposed and developed using well-known xerographic techniques, a second member overcoated with a tacky or tackifiable material is brought into contact with the developed xerographic image. The surface of the tacky material removes the background and the most superficial layer if imaged material from the image member, allowing suflicient toner to remain in the image areas leaving a noise free image upon transfer on the photoconductor. An electrostatic field can be applied in the direction to oppose transfer of the imaged toner that does not make direct physical contact with the tacky surface. The final transfer to a receiver sheet may be either electrostatic or adhesive.

The photoconductive composition utilized may be coated on a substrate or may be dispersed in a binder. Any suitable organic or inorganic photoconductor may be used in the process of the present invention. Typical inorganic photoconductor materials are: sulfur, selenium, zinc sulfide, zinc oxide, Zinc cadmium sulfide, zinc magnesium oxide, cadmium selenide, zinc silicate, calciumstrontium sulfide, cadmium sulfide, mercuric iodide, mercuric oxide, mercuric sulfide, indium trisulfide, gallium triselenide, arsenic disulfide, arsenic trisulfide, arsenic triselenide, antimony trisulfide, cadmium sulfo-selenide and mixtures thereof. Typical organic photoconductors are:

triphenylamine; 2,4-bis(4,4'-diethyl-aminophenyl)-1,3,4-oxadiazo1; N-isopropylcarbazole triphenylpyrrol; 4,S-diphenyl-imidazolidinone; 4,5-diphenylimidazolidinethione; 4,5-bis-(4'-amino-phenyl)-imidazolidinone; 1,5-dicyanonaphthalene; l,4dicyano-naphthalene; aminophthalodinitrile;

nitrophthalodinitrile;

1,2,5 ,G-tetraazacyclooctatetraene- (2,4,6,8 Z-mercapto-benzthiazole; 2-phenyl-4-diphenylidene-oxazolone; 6-hydroxy-2,3di(p-methoxyphenyl)-benzofurane; 4-dimethylamino-benzylidene-benzhydrazide; 3-benzylidene-amino-carbazole;

polyvinyl carbazole;

(Z-nitrobenzylidene)-p-bromo-aniline; 2,4-diphenyl-quinazoline;

1,2,4triazine; 1,5-diphenyl-3-methylpyrazoline;

2- 4'-dimethylamino phenyl -benzoxazole; 3-amino-carbazole;

phthalocyanines and mixtures thereof.

Phthalcoyanine, the subject of copending application Ser. No. 518,450, filed Jan. 3, 1966, is a preferred photoconductor because of its sensitivity and speed. Where it is desired to image directly on the base material zinc oxide is preferred as an inorganic photoconductor because it is rather inexpensive and therefore expendable eliminating the use and need for recycling the photoconductors. Also, it provides a uniform white image support closely resembling ordinary paper surfaces.

Any suitable conductive or non-conductive base may be used in accordance with the process of the present invention. Typical non-conductive bases include: polyurethane, polyvinylidene, polyetylene, polyvinylfiuoride and Mylar, (polyethylenetrephthalate). Typical conductive bases include: NESA glass, aluminized Mylar, conductive polymers, chromium, aluminum, brass, stainless steel, copper, zinc and alloys thereof.

Any suitable tacky or tackifiable substance of the proper viscosity in the range of to 10 poises which properly wets conventional toners or electrostatic marking materials is desirable for use in the present invention. Typical materials include sucrose acetate isobutyrate, resins such as polystyrene, polyterpene, and methyl methacrylate plasticized with non-volatile plasticizer to the viscosity range given above; certain tacky waxes such as Sunoco 5825, a wax from Sun Oil Co. and Lectro-Stik, a wax base adhesive manufactured by Lectrostik Co., Chicago, 111.; and water soluble materials such as gum arabic, gelatins, and polyvinyl alcohols of the proper viscosity manufactured by Union Carbide Corp., 270 Park Ave., New York, N.Y. Of these sucrose acetate isobutyrate and resins such as polystyrene, polyterpene, methyl methacrylate plasticized with non-volatile plastitcizer to the viscosity range given above, and Lectro-Stik, are preferred because they more nearly satisfy the requirements of the present invention. A very useful plasticizer for these organic resins is polyisobutylene. The tacky materials selected must be compatible with the photoconductor employed and chemically unreactive to it. The material may be employed as a plasticizer associated with the photoconductive material or an inert overcoating over the photoconductive material or the matrix suspending the photoconductive material.

Any suitable support substrate, both conductive and nonconductive, may be used in accordance with the present invention. Typical nonconductive bases include polyurethane, polyvinylchloride, polyethyleneterephthalate and polyvinylfluoride. Typical conductive substrates include NESA glass, aluminized Mylar, conductive polymers, chromium, aluminum, brass, stainless steel, copper, zinc and alloys thereof.

The coating in the process of the present invention may consist of a material that is hard and nontacky at normal room conditions which is rendered tacky by heat or solvent vapor after development of the electrostatic image or it may be a tacky substance at normal room conditions. If a tackifiable substance is employed the melting point of the electrostatic marking material must be higher than the tackification temperature of the overcoating. Instead of overcoating the photoconductor with a tacky or tackifiable material, in the case of photoconductor-binder films, the binder itself might be chosen to be tacky or tackifiable.

The coating of the tacky or tackifiable substance may be accomplished by employing conventional methods such as bar coating, dip coating, melt coating, wipe-on coating, pour coating and whirl coating. A preferred method of coating is machine coating because it is easy to employ, it does not involve complicated equipment and it more nearly satisfies the requirements of the present invention. This coating is applied in a thickness of 0.1 to 50 microns. The preferred thickness is just sufficient to trap particles which constitute noise, and which trap a minimum number of particles in image areas. Thicknesses of from /5 to 2 microns are preferable where the coating is applied to a photoconductive imaging surface so that it is necessary that the tacky or tackifiable coating be transparent.

Any conventional charging method may be employed in the process of the present invention when a tackifiable substance is used. If a material which is normally tacky at operating conditions is desired or used, a charging method which does not involve direct contact in order to deposit charge on the adhesive surface should be employed. Suitable non-contact methods include electron gun charging in a vacuum and corona charging in air. Where a tackifiable substance is coated over the photoconductive material direct contact charging methods may be employed. Corona charging is preferred because it may be used where the substance employed over the photoconductive material is tacky or tackifiable normally at room temperature or at normal operating conditions.

Any suitable method of exposure may be employed in practicing the process of the present invention, Where it is desired to utilize a material which is tacky at operating conditions the method of exposure should be one which does not require contact with the adhesive surface. Suitable methods include holographic techniques, non-lens slit scanning systems, and optical projection systems involving lens imaging of opaque-reflection subjects as well as transparent film originals. Reflex and contact exposure systems may be employed when tackifiable xerographic plates are used or when a tacky or tackifiable intermediate transfer or clean-up surface is utilized.

Any suitable development process may be employed in the practice of the present invention. Typical development methods include powder cloud developing, more fully described in U.S. Pats. 2,725,305 and 2,918,910, cascade development, more fully described in ;U.S. Pats. 2,618,551 and 2,618,552, brush, described in U.S. Pats. 2,791,949 and 3,015,305, and touchdown. The preferred method of development is powder development wherein conventional toner particles from about 5 to about 10 microns are applied to about three to four layers thick using the above techniques. If proper image thickness could be provided and the dissolution of the overcoating controlled, liquid development could be considered for use.

Any suitable method of transfer may be employed in the practice of the present invention, Suitable methods include electrostatic transfer and adhesive transfer. It is not desirable to employ adhesive transfer where a normally tacky substance is employed because of possible distortion of the image. With proper control adhesive transfer may be employed where a tackifiable substance is used.

Electrostatic transfer is a preferred method of transfer because it finds uncomplicated use with both tacky and tackifiable substances.

Although in describing the process of the present invention a photoconductive member was specified to obtain the electrostatic image, the electrostatic latent image may be obtained by any suitable method for example, on a dielectric surface by writing with an electron gun in a vacuum, charging through a stencil or charging with a shaped electrode.

Where the tacky substance is applied directly to the photoconductor recycling may be effected by utilizing a thin film of the adhesive substance which may be cleaned using a web cleaner having a solvent for the film in which the toner is suspended. A second overcoating may then be applied. Reapplication of the film may be effected by wipe-on techniques although any of the above suggested techniques may be used.

In the embodiment where a tacky intermediate is used which picks up both the image and the noise retransferring only image and retaining the noise, successful operation in this mode is obtained where the image to noise ratio is greater than one. It is desirable to employ this method where anyone of a variety of photoconductors are desired for use despite their compatibility with the overcoating, their transparency and their hardness at room temperature.

In another mode an adhesive surface is contacted to a developed photoconductor removing all the background and part of the marking material allowing a noise-free image to remain on the developed photoconductor, thus accomplishing the transfer and removal of noise without electrostatic methods. Utilizing this mode it might be desired to impose a field between the photoconductor and the tacky film support to electrostatically repel image toner so as to fracture the image toner in a very thin layer. The field thus imposed repels the image marking material tending to minimize the amount of imaged material removed while electrostatically attracting the oppositively charged marking material in the non-image areas and adhesive removing isolated background particles.

DESCRIPTION OF PREFERRED EMBODIMENTS To further define the specific of the present invention the following examples are intended to illustrate and not to limit the particulars of the present invention. Parts and percentages are by weight unless otherwise indicated.

Example I A selenium xerographic plate is coated with about 1 micron of sucrose acetate isobutyrate using solvent pour coating techniques. After drying to remove the solvent, the plate is corona charged to about 600 volts and selectively illuminated. Two pass cascade development is then employed to develop the plate. The image is then electrostatically transferred to a paper receiver.

Example II A xerographic plate is charged to about 550 volts, selectively illuminated and developed using Xerox Type 10 developer, a commercial cascade carrier and toner. A calendered intermediate plate is then coated with about 4 microns of sucrose acetate isobutyrate using dip coating techniques. After solvent evaporation, the intermediate plate is contacted to the developed xerographic plate. The intermediate plate is then contacted to a grained aluminum lithographic offset master, and corona charges are applied to the paper to repel the image toner to the metal, yielding a high quality, low background offset printing master.

Example III A xerographic plate is charged to about 400 volts selectively illuminated and developed using Xerox 914 toner in a magnetic brush. An intermediate plate is then coated with about 2 microns of sucrose acetate isobutyrate using draw coating techniques. The intermediate plate is then contacted to the developed photoconductor and is corona charged to about 1000 volts to repel the image toner. A paper lithographic master is then contacted to the photoconductor and corona charged to about +1000 volts, whereby a high quality, background-free image is transferred to the master.

Although the present examples are specific in terms of conditions and materials used, any of the above listed typical materials may be substituted when suitable in the above examples with similar results. In addition to the steps used to carry out the process of the present invention, other steps and modifications may be used, if desirable. For example, more than one intermediate roller may be employed to further reduce the amount of background in the final image. In addition, other materials may be incorporated in the adhesive material which will enhance, synergize or otherwise desirably affect the properties of the systems for their present use. For example, the adhesive material may contain an insulating material which may be oppositely charged to the imaged electrostatic marking material so as to minimize the amount of transfer of imaging material with the background.

Anyone skilled in the art will have other modifications occur in the base of the teaching of the present invention. These modifications are intended to be encompassed within the scope of this invention.

What is claimed is:

1. A method of providing an image in an electrostatic process which is substantially free of background, comprising providing an image support member precoated with a tacky layer, forming an electrostatic charge pattern on the surface of said member, developing said charged member with dry electroscopic marking particles to form an image having background, and contacting said developed member to a receiving member to thereby transfer a developed image free of background while retaining the background on the tacky layer. 2. The process as disclosed in claim 1 wherein said image support member comprises a support substrate having superimposed thereon a photoconductive insulating layer, the surface of which is tackifiable.

3. The process as disclosed in claim 1 wherein said layer is tacky under ambient conditions.

4. The process as disclosed in claim 1 wherein said layer is made tackifiable under operating conditions.

' 5. The process as disclosed in claim 1 wherein said image support member is precoated with sucrose acetate isobutyrate.

6. The process as disclosed in claim 2 wherein said layer is made tacky by exposure to a solvent for said tackifiable layer.

7. The process as disclosed in claim 2 wherein said layer is made tacky by exposure to heat.

8. The process as disclosed in claim 1 wherein a fiield is applied between the image support member and the transfer sheet which attracts electroscopic marking particles in the image areas.

9. A method of producing an image in an electrostatic process which is substantially free of background, comprising providing a tacky support member, contacting said support member with an image support member on the surface of which is superimposed an image of dry marking material having background, and transferring the background from said image to the tacky support member.

10. The process of claim 9 wherein more than one tacky support member is contacted to said image support member.

11. The process as disclosed in claim 9 wherein said image support member comprises a support substrate having superimposed thereon a photoconductive insulating layer.

12. The process as disclosed in claim 9 wherein said tacky support member is tacky under ambient conditions.

13. The process as disclosed in claim 9 wherein said tacky member is made tackifiable under operating conditions.

14. The process as disclosed in claim 9 wherein said tacky member is precoated with sucrose acetate isobutyrate.

15. The process as disclosed in claim 9 wherein said layer is made tacky by exposure to a solvent for said tackifiable coating.

16. The process as disclosed in claim 9 wherein said tacky member is made tacky by exposure to heat.

17. The process as disclosed in claim 9 wherein a field is applied between the image support member and the tacky member which repels electroscopic marking particles in the image areas.

18. A method of producing an image in an electrostatic process which is substantially free of background, comprising providing a tacky support member, contacting said support member with an image support member on the surface of which is superimposed an image of dry marking material having background, transferring the image and background to the tacky support member and contacting said tacky support member with the transferred image and background to a receiver to thereby transfer a background-free image to said receiver.

19. The process as disclosed in claim 18 wherein said image support member comprises a support substrate having superimposed thereon a photoconductive insulating layer.

20. The process as disclosed in claim 18 wherein said tacky member is tacky under ambient conditions.

21. The process as disclosed in claim 18 wherein said tacky member is made tackifiable under operating conditions.

22. The process as disclosed in claim 18 wherein said tacky member is precoated with sucrose acetate isobutyrate.

23. The process as disclosed in claim 18 wherein said tacky member is made tacky by exposure to a solvent for said tackifiable layer.

24. The process as disclosed in claim 18 wherein said tacky member is made tacky by exposure to heat.

25. The process as disclosed in claim 18 wherein a field is applied between the tacky support member and the receiver sheet which attracts electroscopic marking materials in the image areas.

26. The process as disclosed in claim 18 wherein more than one tacky support member is contacted in succession before transferring the image to a receiver.

References Cited UNITED STATES PATENTS 2,015,658 10/1935 Beuenberger 117-33 X 2,548,872 4/1951 Cross ct a1 117-33 X 2,857,879 10/1958 Johnson 117-238 X 2,661,289 12/1953 Mayo et a1 117-17.5 X 2,844,123 7/1958 Hayford 117-175 X 3,275,436 9/ 1966 Mayer 96l.4 X 3,352,731 11/1967 Schwertz et al 96l.4 X

OTHER REFERENCES I.B.M. Tech. Dis. Bull., vol. 2, No. 2, Aug. 1959, 96- 1.4, pp. 2 and 3. Bunzey.

WILLIAM D. MARTIN, Primary Examiner B. D. PIANALTO, Assistant Examiner US. Cl. X.R.

961 SD, 1 PC, 96l.4; 117-19, 33 

